JP2019152811A - Optical fiber, coated optical fiber, and optical transmission system - Google Patents

Abstract

To provide an optical fiber capable of easily attaining enlargement of an effective cross-sectional area and an improvement in bending loss characteristics.SOLUTION: An optical fiber 1A comprises: a glass fiber 2A including a core 10 and a cladding 20; a first resin covering layer 31 being in contact with and surrounding the glass fiber 2A; and a second resin covering layer 32 surrounding the first resin covering layer 31 and having a Young's modulus larger than a Young's modulus of the first resin covering layer 31. An effective cross-sectional area at a wavelength of 1550 nm is 110 μmor more and 180 μmor less, a cable cutoff wavelength is 1530 nm or less, and a thickness deviation free ratio of the first resin covering layer 31 is 60% or more and 80% or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical fiber, an optical fiber core, and an optical transmission system.

  In an optical transmission system using an optical fiber as an optical transmission line for transmitting signal light, the optical fiber is required to have low loss and low nonlinearity in order to improve a signal-to-noise ratio (SN ratio). In order to reduce the nonlinearity of the optical fiber, it is effective to increase the effective area of the optical fiber. On the other hand, if the core diameter is increased in order to increase the effective cross-sectional area of the optical fiber, higher-order modes are propagated. Therefore, in order to prevent signal degradation due to interference between modes, the cable cutoff wavelength described in ITU-T G.650.1 is required to be equal to or less than the signal light wavelength, for example, C band (1530 nm to 1565 nm). In the case of propagating the signal light, it is required to be 1530 nm or less.

  A W-type or trench-type refractive index distribution is known as an optical fiber refractive index distribution capable of effectively making a single mode at a wavelength of 1530 nm or more and enlarging an effective cross-sectional area. In these refractive index distributions, only the bending loss of higher-order modes can be increased compared to a simple step-type refractive index distribution, so that the effective area can be increased while maintaining a desired cutoff wavelength. it can.

  Conventionally, the effective area has been increased and the bending loss characteristics have been improved by designing and adjusting the refractive index distribution of the optical fiber (see Non-Patent Documents 1 and 2).

T. Kato et al., Electron. Lett., Vol. 35. pp. 1615-1617, 1999. M. Bigot-Astruc, et al., ECOC’08, paper Mo.4.B.1

  When the effective cross-sectional area is increased and the bending loss characteristics are improved by designing and adjusting the refractive index distribution of the optical fiber, the structure of the optical fiber becomes complicated and mass productivity (manufacturing tolerance) may deteriorate. As a result of diligent research, the inventors have made the resin coating layer surrounding the glass fiber including the core and the cladding into an appropriate cross-sectional shape, thereby increasing the effective cross-sectional area of the optical fiber and improving the bending loss characteristics. I found out that I can plan.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an optical fiber and an optical fiber core wire that can easily increase the effective cross-sectional area and improve the bending loss characteristics. To do. Another object of the present invention is to provide an optical transmission system that includes such an optical fiber as a signal light transmission line and can improve the SN ratio.

An optical fiber of the present invention includes a glass fiber including a core, a clad surrounding the core and having a refractive index lower than the refractive index of the core, and a first resin coating layer surrounding the glass fiber in contact with the glass fiber And a second resin coating layer surrounding the first resin coating layer and having a Young's modulus greater than the Young's modulus of the first resin coating layer. Furthermore, in the optical fiber of the present invention, the effective area at the wavelength of 1550nm is at 110 [mu] m ² or more 180 [mu] m ² or less, the cable cutoff wavelength is less than or equal 1530 nm, no uniform wall thickness ratio of the first resin coating layer 60% 80% or less.

  The optical fiber of the present invention can easily increase the effective area and improve the bending loss characteristics.

FIG. 1 is a diagram showing a cross section and a refractive index distribution of the optical fiber 1A. FIG. 2 is a graph showing the relationship between the ununiform thickness rate of the first resin coating layer 31 and the cable cutoff wavelength. FIG. 3 is a graph showing the relationship between the ununiform thickness ratio of the first resin coating layer 31 and the transmission loss at a wavelength of 1550 nm. FIG. 4 is a diagram showing a cross section and a refractive index distribution of the optical fiber 1B. FIG. 5 is a view showing a cross section of the optical fiber core wire 1C. FIG. 6 is a diagram illustrating a configuration of the optical transmission system 100.

An optical fiber of the present invention includes a glass fiber including a core, a clad surrounding the core and having a refractive index lower than the refractive index of the core, and a first resin coating layer surrounding the glass fiber in contact with the glass fiber And a second resin coating layer surrounding the first resin coating layer and having a Young's modulus greater than the Young's modulus of the first resin coating layer. Furthermore, in the optical fiber of the present invention, the effective area at the wavelength of 1550nm is at 110 [mu] m ² or more 180 [mu] m ² or less, the cable cutoff wavelength is less than or equal 1530 nm, no uniform wall thickness ratio of the first resin coating layer 60% 80% or less.

  In the optical fiber of the present invention, it is preferable that the transmission loss at a wavelength of 1550 nm is 0.174 dB / km or less. An inner cladding that surrounds the core and has a refractive index lower than the refractive index of the core; and an outer cladding that surrounds the inner cladding and has a refractive index lower than the refractive index of the core and higher than the refractive index of the inner cladding. Are preferably included. It is preferable that the core includes a depressed provided at a center, and a ring core surrounding the depressed and having a refractive index higher than that of the depressed.

  The optical fiber core of the present invention includes the above-described optical fiber of the present invention and a colored layer surrounding the second resin coating layer of the optical fiber, and an outer diameter of the colored layer is not less than 180 μm and not more than 210 μm. The optical transmission system of the present invention includes the optical fiber of the present invention as an optical transmission line.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. The present invention is not limited to these exemplifications, but is defined by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

  FIG. 1 is a diagram showing a cross section and a refractive index distribution of the optical fiber 1A. The optical fiber 1A includes a glass fiber 2A mainly composed of silica glass, a first resin coating layer 31 surrounding the glass fiber 2A, and a second resin coating layer 32 surrounding the first resin coating layer 31. . The first resin coating layer 31 and the second resin coating layer 32 are made of an ultraviolet curable resin. The Young's modulus of the second resin coating layer 32 is larger than the Young's modulus of the first resin coating layer 31.

  The glass fiber 2 </ b> A includes a core 10 and a clad 20 that surrounds the core 10. The refractive index of the clad 20 is lower than the refractive index of the core 10. The clad 20 may have a W-type refractive index profile including an inner clad 21 surrounding the core 10 and an outer clad 22 surrounding the inner clad 21. In this case, the refractive index of the inner cladding 21 is lower than the refractive index of the core 10. The refractive index of the outer cladding 22 is lower than the refractive index of the core 10 and higher than the refractive index of the inner cladding 21.

In order to realize such a refractive index profile of the glass fiber 2A, for example, the core 10 is substantially made of pure silica glass, and the cladding 20 is made of silica glass containing fluorine. Alternatively, the core 10 is made of silica glass containing GeO ₂ , the inner cladding 21 is made of silica glass containing fluorine, and the outer cladding 22 is substantially made of pure silica glass.

  When an external force (side pressure) is applied to the optical fiber 1A from the side, the refractive index of the glass fiber 2A changes minutely, and light propagating through the core 10 is coupled to the cladding mode, resulting in leakage loss. Generally, two or more coatings (first resin coating layer 31 and second resin coating layer 32) are provided on the outer periphery of the optical fiber 1A. The first resin coating layer 31 adjacent to the glass fiber 2A is caused by lateral pressure. The influence on the refractive index fluctuation of the glass fiber 2A is large.

  The smaller the difference in effective refractive index between the propagation mode and the cladding mode, the easier the coupling from the propagation mode to the cladding mode occurs. Among the propagation modes, the higher-order mode has a larger effective area than the fundamental mode. Therefore, the effective refractive index of the cladding mode becomes low due to the influence of the cladding 20 having a low refractive index, and the effective refractive index difference between the propagation mode and the cladding mode becomes small. From this, it can be said that the high-order mode is likely to cause leakage loss due to the shape change of the first resin coating layer 31.

  Therefore, by appropriately controlling the shape of the first resin coating layer 31 of the optical fiber 1A in the longitudinal direction, it is possible to selectively increase the higher-order mode scattering loss while keeping the scattering loss of the fundamental mode low. . Thereby, an effective area can be expanded, maintaining a cutoff wavelength in a desired range. The shape control in the longitudinal direction of the first resin coating layer 31 is performed by, for example, adjusting the irradiation time or power of the ultraviolet light irradiated to cure the resin applied to the glass fiber immediately after drawing, or curing the resin by ultraviolet irradiation. This can be easily achieved by adjusting the conditions for winding the optical fiber after being wound around the bobbin.

  An optical fiber 1A having the structure shown in FIG. 1 was manufactured, and the cable cutoff wavelength and transmission loss were evaluated. The outer diameter 2a of the core 10 was 12 μm, and the outer diameter 2b of the inner cladding 21 was 36 μm. For the inner cladding 21, the relative refractive index difference Δ1 of the core 10 was set to 0.32%, and the relative refractive index difference Δ2 of the outer cladding 22 was set to 0.06%. The uneven thickness ratio of the first resin coating layer 31 of the optical fiber 1A was set to various values. The uneven thickness ratio [%] of the first resin coating layer 31 is (minimum thickness / maximum thickness) with respect to the minimum thickness and the maximum thickness in the radial direction of the first resin coating layer 31 in the cross section perpendicular to the fiber axis. S) x100.

  FIG. 2 is a graph showing the relationship between the ununiform thickness rate of the first resin coating layer 31 and the cable cutoff wavelength. As shown in FIG. 2, the cable cutoff wavelength is shortened when the uneven thickness ratio of the first resin coating layer 31 is decreased. FIG. 3 is a graph showing the relationship between the ununiform thickness ratio of the first resin coating layer 31 and the transmission loss at a wavelength of 1550 nm. As shown in FIG. 3, transmission loss increases when the uneven thickness ratio of the first resin coating layer 31 is lower than about 60%. 2 and 3, it can be seen that the effective area can be increased while suppressing an increase in transmission loss by setting the non-uniform wall thickness ratio of the first resin coating layer 31 to approximately 60% or more and 80%. .

Optical fiber 1A has a structure shown in FIG. 1, the effective area at the wavelength of 1550nm is at 110 [mu] m ² or more 180 [mu] m ² or less, the cable cutoff wavelength is less than or equal 1530 nm, non-polarization of the first resin coating layer 31 The meat percentage is 60% or more and 80% or less. Such an optical fiber 1A can easily increase the effective area and improve the bending loss characteristics. Preferably, the transmission loss at a wavelength of 1550 nm is 0.174 dB / km or less.

  The optical fiber having the W-type refractive index distribution has been described above as an example, but the shape of the refractive index distribution is not limited to this. For example, the present technique can be applied to an optical fiber having a refractive index distribution such as a simple step type, a trench type, or a hole providing type. Moreover, the optical fiber 1B which has a structure shown by FIG. 4 may be sufficient.

  FIG. 4 is a diagram showing a cross section and a refractive index distribution of the optical fiber 1B. In the optical fiber 1B shown in this figure, the core 10 of the glass fiber 2B includes a depressed 11 and a ring core 12. The ring core 12 surrounds the depressed 11 provided at the center. The refractive index of the depressed 11 is higher than the refractive index of the outer cladding 22. The refractive index of the ring core 12 is higher than the refractive index of the depressed 11.

In the optical fiber 1B having such a structure, the effective area at the wavelength of 1550nm is at 110 [mu] m ² or more 180 [mu] m ² or less, the cable cutoff wavelength is less than or equal 1530 nm, no uniform wall thickness ratio of the first resin coating layer It is 60% or more and 80% or less. Such an optical fiber 1B can also easily increase the effective area and improve the bending loss characteristics. Preferably, the transmission loss at a wavelength of 1550 nm is 0.174 dB / km or less.

  Further, the optical fiber 1B having such a structure can increase the effective cross-sectional area while maintaining the mode field diameter. That is, the optical fiber 1B can reduce the nonlinearity while suppressing an increase in connection loss with the general-purpose single mode optical fiber.

  FIG. 5 is a view showing a cross section of the optical fiber core wire 1C. The optical fiber core 1C shown in this figure includes a colored layer 33 surrounding the second resin coating layer 32 in the optical fiber 1A shown in FIG. The outer diameter of the colored layer 33 is not less than 180 μm and not more than 210 μm. A normal optical fiber core including a colored layer has an outer diameter of about 250 μm. However, in recent years, an optical fiber core is thinned to an outer diameter of 200 μm to increase the density of an optical cable including a plurality of optical fiber cores. Consideration is being made. Such a thin optical fiber core wire is required to have improved bending loss characteristics. Even if the optical fiber core wire 1 </ b> C of the present embodiment is reduced in diameter, the bending loss characteristics can be improved.

  FIG. 6 is a diagram illustrating a configuration of the optical transmission system 100. In the optical transmission system 100 shown in this figure, for example, C-band signal light transmitted from the optical transmitter 110 is transmitted through the optical transmission path 130 and received by the optical receiver 120. The optical transmission system 100 includes the optical fiber according to the present embodiment as an optical transmission path 130, and the optical transmission path 130 has low loss and low nonlinearity. Thus, the optical transmission system 100 has an improved SN ratio and can transmit a long distance and large capacity signal light.

  DESCRIPTION OF SYMBOLS 1A, 1B ... Optical fiber, 1C ... Optical fiber core wire, 2A, 2B ... Glass fiber, 10 ... Core, 11 ... Depressed, 12 ... Ring core, 20 ... Cladding, 21 ... Inner cladding, 22 ... Outer cladding, 31 ... 1st resin coating layer, 32 ... 2nd resin coating layer, 33 ... Colored layer, 100 ... Optical transmission system, 110 ... Optical transmitter, 120 ... Optical receiver, 130 ... Optical transmission line.

Claims (6)

A glass fiber comprising: a core; and a cladding surrounding the core and having a refractive index lower than that of the core;
A first resin coating layer surrounding the glass fiber in contact with the glass fiber;
A second resin coating layer surrounding the first resin coating layer and having a Young's modulus greater than the Young's modulus of the first resin coating layer;
With
Effective area at the wavelength of 1550nm is at 110 [mu] m ² or more 180 [mu] m ² or less,
The cable cutoff wavelength is 1530 nm or less,
The uneven thickness ratio of the first resin coating layer is 60% or more and 80% or less,
Optical fiber. The transmission loss at a wavelength of 1550 nm is 0.174 dB / km or less.
The optical fiber according to claim 1. An inner cladding that surrounds the core and has a refractive index lower than the refractive index of the core; and an outer cladding that surrounds the inner cladding and has a refractive index lower than the refractive index of the core and higher than the refractive index of the inner cladding. ,including,
The optical fiber according to claim 1 or 2. The core includes a depressed provided in the center, and a ring core surrounding the depressed and having a refractive index higher than that of the depressed.
The optical fiber of any one of Claims 1-3. The optical fiber according to any one of claims 1 to 4, and a colored layer surrounding the second resin coating layer of the optical fiber,
The outer diameter of the colored layer is 180 μm or more and 210 μm or less,
Optical fiber core.   An optical transmission system comprising the optical fiber according to claim 1 as an optical transmission line.

Images